1. Field of the Invention
The present invention relates to a magnetoresistive head and to a perpendicular magnetic recording-reproducing apparatus.
2. Description of the Related Art
In recent years, increase recording density is being rapidly promoted in a magnetic recording medium such as HDD. With increase in the recording density, a size of a record bit recorded in the recording medium is decreased, and intensity in signal magnetic flux is also lowered. Such being the situation, a conventional ring core type inductive magnetic head, which indirectly detects the medium magnetic flux via the ring core by utilizing an electromagnetic induction effect, has come to fail to ensure a sufficient sensitivity relative to lower signal magnetic flux. Under the circumstances, a magnetoresistive head (MR head), which directly senses the medium signal flux by utilizing a magnetoresistance effect, has come to be put to the practical use in recent years.
Nowadays, a spin-valve type MR (SV-MR) head, which has a stacked film of [magnetization pinned layer (pinned layer)/intermediate layer (spacer layer)/magnetization free layer (free layer)] and produces a giant magnetoresistance effect, constitutes the mainstream of the MR head. The SV-MR head produces a giant magnetoresistance effect not smaller than twice that produced by the conventional MR head.
The conventional SV-MR head is constructed such that an SV-MR film is formed between a pair of magnetic shields with a magnetic gap provided therebetween. Also, the conventional SV-MR head uses a so-called current-in-plane (CIP)-MR head in which a sense current supplied by a pair of electrodes is allowed to flow within the plane of the SV film.
Recently, proposed is a so-called current-perpendicular-to-plane (CPP)-MR head, in which a sense current is allowed to flow in a direction perpendicular to the plane of the SV film. The CPP current flow permits further improving a rate of magnetoresistance change (MR change rate), so that a high head output is expected.
On the other hand, in the longitudinal magnetic recording system, improvement in recording density is approaching to the upper limit because of thermal disturbance. As a result, a perpendicular magnetic recording system, which is durable against the thermal disturbance, attracts attentions, and proposed is a system in which the perpendicular recording medium is combined with the SV-MR head.
FIGS. 1A and 1B show schematically constructions of CIP-mode SV-MR heads, which have already been proposed on assumption of use in combination with a perpendicular recording medium. FIGS. 2A and 2B show output waveforms obtained from the SV-MR heads shown in FIGS. 1A and 1B, respectively.
In the conventional systems shown in FIGS. 1A and 1B, what should be considered are an output waveform and reduction of the gap between a pair of magnetic shields. To be more specific, it is desirable that an output waveform having peaks corresponding to magnetization transitions should be obtained as in a conventional longitudinal magnetic recording system. Also, in order to cope with a high recording density expected in the future, it is desirable for the SV film arranged between the magnetic shields to have a small thickness so as to achieve a narrow gap.
FIG. 1A shows a perpendicular magnetic recording system to which a single SV-MR head is applied. As shown in the drawing, the single SV-MR film 10 is arranged to face the perpendicular recording layer 1. The SV-MR film 10 has a stacked structure of [antiferromagnetic layer 11/pinned layer 12/spacer layer 13/free layer 14] as the basic structure, and is arranged between a pair of magnetic shields 15 and 16.
In the system shown in FIG. 1A, obtained is an output waveform that is monotonously changed in accordance with a record bit. In this case, in order to obtain an output waveform having peaks corresponding to magnetization transitions as in the conventional longitudinal magnetic recording system, it is necessary to provide an additional differential circuit to a reproduced signal processing section. However, addition of the differential circuit tends to increase noise. The conventional SV-MR head is also defective in that, since the SV-MR head includes the thick antiferromagnetic layer 11, it is difficult to achieve a narrow gap for coping with high recording density expected in the future.
FIG. 1B shows a perpendicular magnetic: recording system to which a dual striped SV-MR head is applied. As shown in the drawing, a pair of SV-MR films 10 are arranged to face the perpendicular recording layer 1. Each of the SV-MR films 10 is basically equal in construction to the SV-MR film 10 shown in FIG. 1A. The paired SV-MR films 10 are arranged between a pair of magnetic shields 15 and 16 in the system shown in FIG. 1B.
In the system shown in FIG. 1B, the two SV-MR films are differentially operated so as to obtain an output waveform similar to that obtained in the conventional longitudinal magnetic recording system, as shown in FIG. 2B. In the construction shown in FIG. 2B, however, the two SV-MR films are formed within the magnetic gap, which also leads to the problem that it is impossible to cope with high recording density expected in the future.